Among the wide range of magnetic sensors, those based on magnetoresistance (MR) effects are particularly attractive as they combine low cost, small size, and relatively high resolution at room temperature. To date, within the group of MR sensors, anisotropic magnetoresistance (AMR) sensors have the best resolution. Other promising results were obtained for example by using an ensemble of tunneling magnetoresistance (TMR) sensors or by the integration of Micro Electro Mechanical System (MEMS) flux concentrators.
Planar Hall effect (PHE) sensors [(1) Mor V, Schultz M, Sinwani O, Grosz A, Paperno E, and Klein L (2012), “Planar Hall effect sensors with shape-induced effective single domain behavior,” J. Appl. Phys., vol. 111, 07E519, doi:10.1063/1.3680084; (2) Persson A, Bejhed R S, Østerberg F W, Gunnarsson K, Nguyen H, Rizzi G, Hansen M F, Svedlindh P (2013), “Modelling and design of planar Hall effect bridge sensors for low-frequency applications,” Sensors and Actuators A, vol. 189, pp. 459-465, doi: 10.1016/j.sna.2012.10.037; and (3) Schuhl A, Nguyen Van Dau F, Childress J R (1995), “Low-field magnetic sensors based on the planar Hall effect,” Appl. Phys. Lett., vol. 66, pp. 2751-2753, doi: 10.1063/1.113697] have important intrinsic advantages compared to AMR sensors. PHE sensors are less sensitive to temperature drift [(3) above], which limits the resolution at low frequencies. They are also much simpler compared to TMR or giant magnetoresistance sensors, which comprise a stack of layers fabricated in complex processes. Such a layer stack also results in additional sources of noise, which is difficult to control and suppress [Lei Z Q, Li G J, Egelhoff W F, Lai P T, Pong P W T (2011), “Review of noise sources in magnetic tunnel junction sensors,” IEEE Trans. Magn., vol. 47, pp. 602-612, doi: 10.1109/TMAG.2010.2100814].
Despite the advantages, so far the reported resolution of PHE sensors is lower than that of AMR sensors.
Therefore, there is a long-felt need to provide planar Hall effect sensors that will manifest their intrinsic advantages. A very important factor that determines the sensitivity of the sensor is the direction of the easy magnetic axis and the magnitude of the magnetic anisotropy field. In addition, it is important to minimize the noise. This invention describes a method of fabricating PHE sensors where these properties are determined by the shape and size of the sensing area; therefore, they are easily tailor-made with predetermined properties. Furthermore, multiple sensors with different properties can be easily fabricated on a single chip thus opening the way for more complicated devices that will achieve extended operational range and simultaneous measurement of the two components of the magnetic field in the chip plane. The invention also describes methods for decreasing the noise which comprise of choosing an excitation current with appropriate amplitude and frequency.